Reconciling reported and unreported HFC emissions with atmospheric observations

Abstract

We infer global and regional emissions of five of the most abundant hydrofluorocarbons (HFCs) using atmospheric measurements from the Advanced Global Atmospheric Gases Experiment and the National Institute for Environmental Studies, Japan, networks. We find that the total CO 2 -equivalent emissions of the five HFCs from countries that are required to provide detailed, annual reports to the United Nations Framework Convention on Climate Change (UNFCCC) increased from 198 (175-221) Tg-CO 2 -eq·y -1 in 2007 to 275 (246-304) Tg-CO 2 -eq·y -1 in 2012. These global warming potential-weighted aggregated emissions agree well with those reported to the UNFCCC throughout this period and indicate that the gap between reported emissions and global HFC emissions derived from atmospheric trends is almost entirely due to emissions from nonreporting countries. However, our measurementbased estimates of individual HFC species suggest that emissions, from reporting countries, of the most abundant HFC, HFC-134a, were only 79% (63-95%) of the UNFCCC inventory total, while other HFC emissions were significantly greater than the reported values. These results suggest that there are inaccuracies in the reporting methods for individual HFCs, which appear to cancel when aggregated together.halocarbons | radiative forcing | climate change

Global and regional emissions estimates of 1,1-difluoroethane (HFC-152a, CH<sub>3</sub>CHF<sub>2</sub>) from in situ and air archive observations

“…East Asia and Europe contribute emissions of ∼ 7 and ∼ 6 Gg yr −1 , respectively to the global total. The 2007-2009 North American emission estimate of 28 Gg yr −1 agrees within the uncertainties of HFC-152a emission estimates reported in Barletta et al (2011) and Simmonds et al (2015). The North American estimate indicates one reason why the UNFCCC reported amount appears to be so low; more than half the global emissions appear to come from this continental region, yet the UNFCCC reports do not include specific HFC-152a emissions from the US.…”

“…We used the methodology outlined in Lunt et al (2015) and Rigby et al (2011b) to derive emissions of HFC-152a from continental regions. The high-resolution, regional UK Met Office Numerical Atmospheric-dispersion Modelling Environment (NAME), Manning et al (2011) was used to simulate atmospheric HFC transport close to a subset of AGAGE monitoring sites, which were strongly influenced by regional HFC sources (domains shown by red boxes in Fig.…”

“…We estimated annual emissions for the period 2007-2012 and aggregated the derived emissions fields into continental regions, separating countries that either do ("Annex-1"), or do not ("non-Annex-1") report detailed, annual emissions to the UNFCCC. Emissions were estimated using a hierarchical Bayesian inverse method (Ganesan et al, 2014;Lunt et al, 2015) and all high-frequency observations from 10 of the 11 sites listed in Table 1, excluding Shangdianzi due to the short time series. The hierarchical Bayesian method includes uncertainty parameters (e.g., model "mismatch" errors and a priori uncertainties) in the estimation scheme, reducing the influence of subjective choices on the outcome of the inversion.…”

“…Europe, United States, Asia, and Australia Lunt et al (2015) have reported global and regional emissions estimates for the most abundant HFCs, based on inversions of atmospheric mole fraction data, aggregated into two categories; those from Annex 1 countries and those from non-Annex 1 countries. The inversion methodology used the NAME model to simulate atmospheric transport close to the monitoring sites, and the Model for Ozone and Related chemical Tracers (MOZART, Emmons et al, 2010) to simultaneously calculate the effect of changes to the global emissions field on each measurement site.…”

“…For example, emissions reported by the USA to the UNFCCC for HFC152a, 227ea, 245ca and 43-10mee are shown in the database as "commercially confidential", and they constitute the aggregated "unspecified" emissions. HFC-152a emissions from the USA are estimated to be the primary contributor to the total for this gas from Annex 1 countries (Lunt et al, 2015). Previous papers Millet et al, 2009;Stohl et al, 2009;Barletta et al, 2011;Miller et al, 2012;Simmonds et al, 2015) have reported major differences between USA HFC-152a emission estimates derived from atmospheric measurements (top down) and emissions calculated from US reports to the UNFCCC (bottom up).…”